Many medical situations and treatments are associated with the need for conveying fluid media into or out of the body of a patient. Access to a person's circulatory system, such as the cardiovascular or the cerebrospinal fluid system, is often achieved by means of introducing a catheter tube into the patient in a subcutaneous, intravascular or intramuscular way. Insertion of a catheter is done by means of a needle element, wherein the needle point is used for punctuating e.g. a vein and subsequently introducing the catheter before withdrawing the needle, leaving only the soft catheter tube which for instance may be connected to a source of fluid to be administered into or from the vein.
A typical example of such medical situation is blood dialysis (usually hemo-dialysis), which sometimes is required as a consequence of kidney malfunction. In dialysis, two catheter tubes are inserted into a so called fistula which is created by connecting an artery to a vein. One catheter is used for withdrawal of blood and the other for reinserting it into the patient. Dialysis treatment is a rather delicate and exposed situation for the patient and it is desired to provide a very cautious and careful handling during the penetration of the patient's skin or fistula wall or during the continued treatment.
A common problem related to dialysis treatment (as well as to any situation involving insertion procedure for a catheter tube) is the risk of blood leakage, particularly when connecting the dialysis equipment to the fistula. Typically, the needle used for connecting the assembly to a fistula has quite a large diameter (often larger than 1.6 mm) in order to provide for sufficient volume of blood passage during the time dialysis is run, and at the same time avoiding rupture of the blood cells which are passing at a high flow rate. The large needle in combination with the high pressure in a fistula leads to the risk that blood from the circulation system often escapes, either when connecting the catheter to the fistula or during treatment, resulting in a leakage of blood which is of course highly undesired as it makes an already uneasy and exposed situation even worse for the patient, and also leads to a risk for blood contamination for health care providers.
As the blood pressure within a fistula is very high, penetration will lead to a heavy and immediate outflow of blood. This naturally puts extremely high demands on the equipment/catheter assemblies which are intended to be used for transferring the blood from the patient to the dialysis equipment and again back to the patient. A catheter assembly used in dialysis should be designed to handle over—as well as subpressure since each fistula is connected to two catheters: one for the withdrawal of blood and one for reintroducing it into the patient. The assembly through which blood will be withdrawn will be subjected to a subpressure and the assembly through which blood is to be transferred back to the patient will be subjected to a overpressure. In each of those situations there is a risks that the pressure difference inside the catheter hub compared to the ambient pressure leads to failure of the assembly components with leakage as consequence.
Another risk associated with extracorporal treatment is the occurrence of turbulence in the blood flow leading to risk of damage to the blood cells (hemolysis) which, as a result of the frequently reoccurring treatments that the patient is subjected to, gradually would degenerate the patient blood and in the long run represent a serious health risk.
Another problem which may pose a serious problem during a dialysis treatment is the risk of clotted/coagulated blood which sometimes is formed inside the catheter introducer assembly running the risk of entering into the dialysis equipment and/or into the patients. A blood clot unintentionally entering a blood circulation system of a patient could lead to serious health risks and even be fatal.
In one type of catheter assembly, the fistula is penetrated by a needle which is subsequently withdrawn only leaving the catheter tube for transferral of blood or liquid. This is advantageous since a soft catheter tube will not run the risk of damaging the patient's fistula/skin the way a dialysis needle could. However, retracting the cannula (often a metal needle) out of the instrument sometimes gives rise to undesired friction drag between the needle and the assembly wherefrom it is to be removed, which in its turn may lead to an inert or even irregular retraction motion which is of course a disadvantage: preferably connection of a catheter tube should be performed smoothly and without sudden interruptions.
Many examples of sealing devices for assemblies exist, aiming to prevent leakage in various forms, e.g. leakage of blood. For instance in U.S. Pat. No. 4,960,412, there is seen a catheter introducing system with a so called “duckbill”-solution, and in U.S. Pat. No. 5,403,284 there is described an automatic shut-off mechanism for a catheter tube assembly. However due to the specific circumstances related to certain treatments such as dialysis, according to our knowledge, no prior art arrangement has yet presented a fully satisfactory solution for connecting to a catheter assembly. Existing catheter introducing assemblies are often quite complicated to handle, and may e.g. require at least two hands during the introducing procedure which makes the connection of the catheter laborious for the professional health care provider as well as it eliminates the possibility of self-treatment at home: the operation is simply too difficult to perform by oneself.